Stretched 2X modes exist. My monitor goes down to 800x600 and I can use the 400x300 stretch. I expect 400 is the minimum it can go without crashing.

I experimented once with motion blur in the Quake2 software engine, simply by blending old and new frames. Movement is so fast that it leaves a lot of artifacts when turning quickly. It may have looked better with multiple frames generated per displayed frames.